Press apparatus for dewatering a fiber web

ABSTRACT

APPARATUS FOR DEWATERING A FIBER WEB CARRIED ON A MOVING FORMINOUS WIRE ON WHICH THE WEB WAS FORMED COMPRISING A WIRE OR FELT OVERLYING THE FORAMINOUS WIRE AND MOVABLE CONIOINTLY WITH IT ALONG A PORTION OF ITS TRAVEL AND PRESS PALTES POSITIONED ON EITHER SIDE OF THE WIRE AND THE OVERLYING WIRE OR FELT TO ENGAGE AND SQUEEZE THE FIBER WEB BETWEEN THEM TO EXPRESS WATER FROM THE WEB IN THE ZONE OF PRESSURE BETWEEN THE PLATES. ONE OF THE PRESS PLATES IS MOUNTED, SUCH AS BY MEANS OF A LEVER, FOR LINEAR MOVEMENT TOWARD AND AWAY FROM THE OTHER PRESS PLATE AND SUCH AS BY MEANS OF A PIVOT MOUNTING FOR ATTACHING THE PRESS PLATE TO THE LEVER, FOR ANGULAR   MOVEMENT OF ITS MAJOR PLANE RELATIVE TO THE MAJOR PLANE OF THE OTHER PRESS PLATE. THE MOVABLE PRESS PLATE IS URGED TOWARD THE OTHER PRESS PLATE WITH A PREDETERMINED ADJUSTABLE FORCE EFFECTIVE TO CREATE A ZONE OF PRESSURE IN THE WEB OF WHICH (A) THE INTEGRATED MAGNITUDE OVER THE AREA OF THE PLATES IS SUBSTANTIALLY CONSTANT AND (B) THE DISTRIBUTION CURVE IN THE DIRECTION OF MOVEMENT OF THE WEB IS OF SUBSTANTIALLY UNALTERED SHAPE, REGARDLESS OF TRANSIENT VARIATIONS IN THE THICKNESS AND DRAINAGE PROPERTIES OF THE WEB.

Jan. 19, 1971 E. G. STENBERG 3,5563% PRESS APPARATUS FOR DEWATERING A FIBER Filed Aug. 31, 1967 2 Sheets-Sheet l INVENTOR. ERIK GUNNAR STENBERG his ATTORNEYS.

1 9; 1 E. G. STENBERG 3,

PRESS APPARATUS FOR DEWATERING-A FIBER WEB Filed Aug. 31, 1967 2 Sheets-Sheet 2 Fig.3

INVENTOR. ERIK GUNNAR STENBERG his ATTORNEYS.

United States Patent 3,556,939 PRESS APPARATUS FOR DEWATERING A FIBER WEB Erik Gunnar Stenberg, Karlstad, Sweden, assignor to Aktiebolaget Karlstads Mekaniska Werkstad, Karlstad, Sweden, :1 company of Sweden Filed Aug. 31, 1967, Ser. No. 664,737

Claims priority, application Sweden, Sept. 9, 1966,

Int. Cl. DZlf 1/38 US. Cl. 162-313 9 Claims ABSTRACT OF THE DISCLOSURE Apparatus for dewatering a fiber web carried on a moving foraminous wire on which the web was formed comprising a wire or felt overlying the foraminous wire and movable conjointly with it along a portion of its travel and press plates positioned on either side of the Wire and the overlying wire or felt to engage and squeeze the fiber web between them to express water from the web in the zone of pressure between the plates. One of the press plates is mounted, such as by means of a lever, for linear movement toward and away from the other press plate and, such as by means of a pivot mounting for attaching the press plate to the lever, for angular movement of its major plane relative to the major plane of the other press plate. The movable press plate is urged toward the other press plate with a predetermined adjustable force effective to create a zone of pressure in the web of which (a) the integrated magnitude over the area of the plates is substantially constant and (b) the distribution curve in the direction of movement of the web is of substantially unaltered shape, regardless of transient variations in the thickness and drainage properties of the web.

BACKGROUND OF THE INVENTION This invention relates to the dewatering of a fiber web and, more particularly, to a novel and improved press apparatus for dewatering a fiber web of board stock as it moves along on the foraminous wire on which it was formed.

In the usual type of board machine a continuous fiber web is produced by draining a fiber suspension on an endless foraminous wire runrn'ng over one or more kinds of dewatering devices, such as table rolls, drainage strips and suction boxes. A fiber web of board stock produced in a board machine is often relatively thick and has such a higher water content that additional drainage is necessary before it can be subjected, without danger of damage, to pressing in, for example, conventional press rolls. The web requires a relatively long pressing time and the narrow bands of pressure afforded by the nip between press rolls does not provide a pressing time of suificient duration. Moreover, the press load must be limited, because the water pressed out at the nip will fiow in the plane of the web in the opposite direction to the web travel. If the velocity of water fiow in the web becomes too high, hydraulic forces will cause the web to be wholly or partially broken up, an effect known generally as crushing.

It is known, per se, that the water content of a fiber web can be reduced by pressing it before it is transferred from the wire and delivered to conventional press devices, and several different kinds of devices have been used or suggested for this purpose.

In some types of known prepressing devices the web is pressed between the wire on which it was formed and a top wire, the two wires forming a number of dewatering nips between a series of press rolls arranged in pairs with one roll on either side of the wires. The pressing time in each one of these nips is short, and there are large pressure gradients in the plane of the web. Crushing can occur at each nip and impair the quality of the web without necessarily destroying it completely. Other types of prepressing devices embody a nip of fixed shape between press plates that are frequently enclosed by endless wires or steel belts. In some cases the shape of the nip is fixed by endless belts provided with smooth or perforated press plates moving in the direction of travel of the wire. The compressive force in these nips, which are of fixed shape, is adjusted to varying magnitudes, depending in variations in the properties of the web (thickness, quality, etc.). Even a very small transient increase in the basis weight of the web can cause a substantial increase in the pressure gradients, resulting in crushing that is difiicult to detect.

In the above-mentioned devices, the press plates or the endless belts are usually mounted to form a tapered nip so that the fiber web is subjected to higher compressive force as it is carried forward by the driven wires. In some cases the top wire can be replaced by a felt. In general, the previously known techniques and devices for draining a travelling :fiber web by applying continuous squeeze pressure to it give highly varying results that are difiicult to control quickly. Many of the devices are inefiicient or complicated.

SUMMARY OF THE INVENTION The primary objective of the present invention is to achieve continuous wet pressing of a fiber Web of board stock by means of a reliable, efficient pressing device of simple, trouble-free construction. Before describing the structure and operation of the press device of the invention, it is useful to consider first the theory underlying dewatering under pressure. The magnitude and distribution of the compression pressure in a press nip is usually illustrated by a pressure distribution curve. For a satisfactory pressing operation, it is desirable that the requisite compression pressure be attained without the pressure rise and the pressure gradient reaching such values that the web is damaged. For a given application, it can be established fairly well how the pressure distribution curve should appear if it is to represent a favorable pressing operation. When pressing a travelling fiber web in a press nip between two pressplates which are stationary relative to the direction of travel of the web and one of which is fixed and parallel to the direction of travel of the web and the other is movable relative to the first as to both angle and distance, the shape of the pressure distribution curve will be determined by a number of factors, such as the basis weight, moisture content, dynamic compression properties and velocity of the web, the profile of the press plates, the vertical angular position of the movable press plate relative to the plane of travel of the web, and the distance of the movable press plate from the fixed press plate. The same factors have the same fundamental importance in the case where both the press plates are movable in relation to each other as regards angle and distance.

Of the above-mentioned factors, only the angular position and the distance can, as a practical manner, be controlled in the actual pressing operation. If external, variable forces are caused to actuate the movable press plate, its angular position and distance can be controlled, and the appearance of the pressure distribution curve can thereby be altered within certain limits. If any of the web properties are altered during pressing, this 'will cause a change in the pressure distribution curve. By suitable control of angular position and distance of the movable press plate, however, such changes of the pressure distribution curve can be counteracted, so that it retains an essentially unaltered appearance. In a press device according to the present invention, as described Patented Jan. 19, 1971 below, both the angular position and distance of the movable press plate relative to the fixed press plate can be controlled within wide limits.

The apparatus for dewatering a fiber web, in accordance with the invention, comprises a belt, preferably a wire or felt, arranged to move conjointly with the wire along a portion of its travel and press plates positioned on either side of the belt and wire to create a zone of pressure between them to squeeze water from the web. The press plates are stationary in the direction of movement of the web, but one or both of them is mounted for movement in a direction toward and away from the other and for angular movement of its major plane relative to the major plane of the other. The movable press plate is urged toward the other press plate with a predetermined, adjustable force effective to exert a pressure on the Web of which (a) the integrated magnitude, over the area of the plate is substantially constant and (b) the distribution curve in the direction of movement of the web is of substantially unaltered shape, both of these conditions being maintained regardless of transient variations in the thickness and drainage properties of the Web.

In a preferred embodiment of the invention, the movable press plate is carried by a lever that is pivoted about an axis substantially perpendicular to the direction of movement of the web, the axis preferably being located downstream from the transverse center-line of the movable press plate, and is mounted for pivotal movement on the lever about a second axis parallel to the first axis, the second axis being downstream of the transverse center-line of the movable press plate. The lever is urged in a direction to pivot it about its axis such that the movable press plate is moved toward the other press plate with a predetermined force, thereby creating a zone of pressure, the integrated magnitude of which is substantially constant over the area of the plates. Further, the movable press plate is pivoted about the second axis, such as by means of a pressure cylinder acting between the trailing end of the movable press plate and the lever which carries it, thereby providing a pressure gradient in the pressure zone in which the pressure increases in the downstream direction, relative to the movement of the fiber web.

The shape of the pressure distribution curve can be established to meet a desired result by appropriately shaping the faces of the press plates so that the pressure zone between the press plates has a predetermined dimensional gradient along the direction of movement of the fiber Web.

At least one of the press plates, and advantageously both, is perforated and provided with grooves on its inside face to facilitate the collection and drainage of Water removed by the apparatus.

The apparatus of the invention operates essentially as follows: First of all, the dimensions of the pressure Zone, both as to area and ot thickness variation in the direction of movement of the Web are preestablished by the dimensions and surface contours of the press plates.

With a given area and thickness dimension gradient of the pressure Zone, the integrated pressure across the entire area of the pressure zone and the distribution of pressure in the pressure zone are established at predetermined adjustable values. In particular, the gradient of pressure in the pressure zone between the press plates is established by the magnitude of the adjustable force that pivots the movable press plate about its pivot axis mounting on the lever, thus creating a movement of the-plate about the pivot axis, the extent of which determines the degree to which the hydrostatic pressure in the fiber web increases as it passes through the pressure zone. With relatively higher values of the force creating pivotal movement of the press plate about its pivot axis mounting, the pressure distribution curve is, of course, steeper than for relatively lower values. Thus, by varying the pivoting force between lower and higher values, the shape of the distribution curve is altered appropriately to provide a desired pressure gradient in the pressure zone.

The integrated magnitude of the pressure in the pressure zone over the area of the press plates is established by the force urging the lever about its pivot axis to move the movable press plate toward the other press p ate. This force is transmitted to the movable press plate through the pivot mounting by which it is carried by the lever, the pivot mounting axis preferably being downstream from the transverse center line of the press plate. Accordingly, the force is applied to the plate at a position such that the pressure gradient increases in the downstream direction. By varying the force applied through the lever to the plate, the integrated magnitude over the area of the plate of the pressure in the pressure zone is appropriately adjusted to a desired value and is maintained at that value, regardless of transient variations in the thickness and drainage properties of the web. Thus, by decreasing the force acting on the press plate, the integrated magnitude of pressure in the pressure zone is reduced, whereas an increase in the force increases the integrated magnitude of pressure.

The press apparatus, according to the invention, provides a number of advantages. For one thing, the shape of pressure zone can be varied, and the pressure can be adjusted over a considerable range, both as to the integrated magnitude of pressure over the entire area of the plates and as to the distribution of pressure. Because the apparatus provides excellent control of both the magnitude and distribution of pressure in the pressure zone, the risk of any crushing of the fiber web is considerably reduced. A further advantage resides in the fact that the pressure plates may be of substantial area, thereby increasing the pressing time and consequently the effectiveness of dewatering in the press apparatus. If desired, additional press plate pairs can be provided in a given unit, and several units can be used in a machine.

The water removed by the press apparatus flows through the fiber web in a substantially right angle to its plane and thence to the perforated press plate or, where both press plates are perforated, through both of them. Accordingly, the compression pressure can be maintained at a relatively high value without risk of crushing. Inasmuch as the press plates are stationery in the direction of movement of the web, the water removed by the apparatus will remain in a fixed zone and can be conducted away from the press plates relatively quickly and easily. The absence of any tendency for the web to be rewet by the water removed, as is the case with moving press plates, provides, particularly in conjunction with the other adv'antages'of the apparatus, a dryness in the web that is considerably higher than can be obtained using apparatus previously known in the rt.

For better understanding the invention, reference made to the following description of an exemplary embodiment, taken in conjunction with the figures of the accompanying drawings, in which:

FIG. 1 is a side elevational view, in generally schematic form, showing a board machine embodying the press apparatus .of the invention;

FIG. 21s a side elevational view, also in generally schematic form, showing the press apparatus embodied in the machine of FIG. 1 but on a larger scale than FIG. 1;

FIG. 3 is anenlarged, fragmentary plan view of the inside face surface of a press plate embodied in the press apparatus of FIGS. 1 and 2; and

FIG. 4 is a cross-sectional view of a portion of one of the press plates, the view being taken generally along the lines 4-4 of FIG. 3 and in the direction of the arrows.

1 DESCRIPTION OF AN EXEMPLARY 1 EMBODIMENT The embodiment of the invention described below and shown in the drawings is intended to be merely exemplary,

and those skilled in the art will be able to make numerous variations and modifications of it without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as defined in the appended claims.

FIG. 1 shows a board machine fitted with a headbox 1 and deckle boards 3 arranged to deposit and spread a suspension of board stock on an endless bottom foraminous wire 5. The bottom wire 5 is supported by three endless power fabrics 7, which run over guide rolls 9 and stretch rolls 11, and passes around the bottom roll 13 of a couch press 15 and then over guide rolls 17, stretch rolls 19 and a wire regulating device 21. Suction boxes 23 are positioned within the loops of the power fabrics 7. Other kinds of drainage devices, such as table rolls and drainage strips, can also be arranged in suitable positions above the wire. An endless top wire 25 is arranged to run in a loop around the top roll 27 of the couch press 15 and then around a guide roll 29 and a stretch roll 31. The top wire 25"can be, if desired, replaced by a felt. A press constructed according to the invention, which is designated generally by the reference numeral 33, is located upstream from the couch press 15.

As shown in more detail in FIG. 2, the press 33 comprises a perforated bottom press plate 35 and a perforated top press plate 37. Both the press plates 35 and 37 are shown as being flat, but they might well be curved so as to obtain a desired pressure distribution curve. The bottom press plate 35 is rigidly connected to a stationary frame 39, while the top press plate 37 is pivotally mounted on pins 41 in two transversely spaced, parallel levers 43, so that the axis of rotation of plate 37 is horizontal and at right angles to the direction of travel of the wires 5, 7 and 25. The axis of rotation of press plate 37 is located somewhat downstream from the geometrical center line of the press plate 37 in the transverse direction relative to direction of travel of the wires 5, 7 and 25. Each lever 43 is pivotally mounted by a pin 45 in the fixed frame 39.

Two pneumatic pressure devices 47 are arranged between the rear part of the top plate 37, i.e., the downstream part relative to the direction of travel of the wires 5, 7, 25 and the two levers 43. The frame 39 is provided with two hydraulic pressure devices 49, each of which is fitted with a piston rod 51. The piston rods 51 are pivotally connected to the levers 43 by means of pins 53. The pressure devices 47 and 49 can be pneumatic, hydraulic or mechanical.

The two press plates 35 and 37, in conjunction with the power fabric 7, bottom wire 5 and top wire 25, form a press nip 55 for the fiber web 57 that is formed and conveyed on the bottom wire 5. The press plates 35 and 37 are perforated and provided with troughs or gutters 59 to carry off water which extend across the machine and therefore discharge outside the edges of the wires 5, 7 and 25 FIGS. 3 and 4 show the structure of the bottom press plate 35 in more detail as including a large number of holes 61, oriented principally at right angles to the surface of the plate 35 and arranged in a suitable pattern. It is essential that the holes 61 be large enough and pitched close enough together so that the total resistance to flow of the water of the fiber web 57 through the web 57, the wires 5 and 7 and out through the holes 61 is lower essentially at right angles to the plane of the web 57 than in any other direction. To facilitate the movement of water to the holes 61, the surface of the plate 35 facing the wire 7 is provided with grooves 63 which interconnect the holes 61.

The board machine described in the foregoing paragraphs operates in the following manner: for production of board, a suspension of board stock is deposited from the headbox 1 and spread uniformly over the moving bottom 'wire 5. The suspension is drained through the bottom wire 5 and forms a continuous mat or web of fibers 57. The fiber web 57 is carried on the bottom wire 5 through the press 33 and the couch press 15, after which it is taken off the bottom wire 5 for further treatment. In the press 33 the fiber web 57, together with the bottom wire 5, the power fabric 7 and the top wire 25, passes through the press nip 55 between the two press plates 35 and 37. Forces of adjustable magnitude for controlling the movable press plate 37 to provide a desired pressure between the press plates are produced by supplying pressure to the pressure devices 47 and 49 from suitable sources. The forces created by the pressure devices 47 and 49 produce 'both pressure and a tendency for pivotal movement on the press plate 37 about its pivot mounting pins.

The force from the pressure device 49 is transmitted by the piston rod 51 and the pin 53 to the lever 43, and imparts to the lever 43 a counterclockwise (with respect to FIG. 2) turning moment about the pin 45. This moment is counteracted by clockwise reactive turning moment on the lever 43 about the pin 45 due to a restoring force exerted by the resistance to pressure of the fiber mat in the press nip acting through the press plate 37 and the pin 41, and a second restoring force from the pressure device 47. A given value of the restoring force through the pin 41 'will correspond to given values of the forces from the pressure devices 47 and 49 when the lever 43 is in equilibrium. By controlling the forces provided by the pressure device 47 and 49, each of the restoring forces directed through pressure device 47 and pin 41 is established at a predetermined value. These restoring forces are balanced by external forces on the press plate 37, and the sum of these determines the total magnitude of the pressure created by the press 33 on the fiber web 57.

The magnitude of the several external forces acting on the system determines the position of their resultant between the pin 41 and the pressure device 47 on the rear edge of the press plate 37. The resultant of the external forces produces a turning moment on the press plate 37 about the pin 41. This moment in turn causes the press plate 37 to assume an angular position in which it balances the turning moment that the restoring forces from fiber web 57 exert on the press plate 37. The angular orientation of the movable press plate 37 relative to the fixed press plate 35 and the distance between the press plates are determined by the relationship between the adjustable forces created by the pressure devices 47 and 49 and the restoring forces from the fiber web 57 in the press nip 55 acting on the press plate 37. For set values of force provided by the pressure devices 47 and 49, the movable press plate 37 shifts toward or away from the fixed plate and changes its angular orientation so that the restoring forces return the press to an equilibrium condition upon any change in the characteristics of the fiber mat 55. Accordingly, the magnitude of the integrated pressure in the press nip 55 during pressing remains substantially constant, and the pressure distribution curve retains an essentially unchanged shape.

I claim:

1. Apparatus for dewatering a fiber web carried on a moving foraminous wire on which it was formed comprising a belt movable conjointly with the wire and disposed adjacent the wire along a part of its traverse with the fiber web between it and the wire, first and second press plates positioned generally opposite each other and/or either side of the web with said wire and belt arranged to engage and squeeze water from the web in a pressure zone between said plates as the web passes therethrough, said plates being stationary relative to the direction of movement of the web, wire and belt, means mounting the first press plate for linear movement in a direction toward and away from the second press plate, means mounting the first press plate for angular movement of its major plane relative to the major plane of the other press plate independently of the linear movement of the first press plate toward and away from the second press plate, and means for urging the first press plate toward the second press plate with a predetermined adjustable force, whereby the first and second press plates exert in the pressure zone a pressure on the web having (a) a predetermined integrated magnitude over the area of the plates and (b) a distribution of pressure in the direction of movement of the web corresponding to a distribution curve of substantially uniform shape, regardless of transient variations in the thickness and drainage properties of the web.

2. Apparatus according to claim 1 wherein the means for urging the first press plate towards the second press plate includes means for imposing a force of adjustable magnitude on the first press plate at a point of application which is downstream with respect to the direction of travel of the web from the transverse center line of the first press plate, thus maintaining the angular orientation of the movable press plate at an equilibrium position which provides a pressure gradient of increasing magnitude in the downstream direction, relative to the movement of the web.

3. Apparatus according to claim 1 wherein at least one of the press plates is perforated.

4. Apparatus according to claim 1 wherein the belt is porous.

5. Apparatus according to claim 2 wherein the means for mounting the first press plate for movement toward to second press plate includes a lever mounted for pivotal movement about a fixed first pivot axis disposed substantially perpendicular to the direction of movement of the web, wherein the means for mounting the first press plate for angular movement includes means pivotally mounting the movable press plate on the lever for pivotal movement about a second axis parallel to the first axis, and wherein the pivot mounting is the point of application of pressure on the first press plate.

6. Apparatus according to claim 5 wherein the first axis is downstream from the second axis.

7. Apparatus according to claim 5 wherein the means urging the first press plate toward the second press plate includes pressure means coupled to the lever for pivoting the lever in a direction to urge the first press plate toward the second press plate with an adjustable predetermined force acting at the second axis.

8. Apparatus according to claim 7 wherein the means urging the first press plate toward the second press plate further includes pressure means acting between the first press plate and the lever at a point downstream from the second axis for pivoting the first press plate relative to the lever about the second axis, whereby a gradient of pressure of increasing magnitude in the downstream direction is established in the web as it passes through the zone between the press plates.

9. Apparatus according to claim 3 wherein the perforated press plate has a multiplicity of spaced-apart orifices extending through the plate and grooves formed in the surface facing the pressure zone and interconnecting the holes.

References Cited UNITED STATES PATENTS 1,723,051 8/1929 Mantius 162-312X 2,783,689 3/1957 Skoldkvist l62313 3,215,593 11/1965 Green 162301 REUBEN FRIEDMAN, Primary Examiner T. A. GRANGER, Assistant Examiner U.S. Cl. X.R. 162-361 3 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,555,939 Dated January 19, 1971 Inventor(s) E. G. STENBERG It is certified that error appears in the above-identified paten and that said Letters Patent are hereby corrected as shown below:

Column 1, line 51, "higher" should be -high-. Column 2, line 11, "in" should be -on-; line 44, "pressplates" should be two words. Column 3, line 57 "ot" should be -to-. Column 6, line 63, "and/or" should be --and on. Column 7, line 26 "to" should be -the.

Signed and sealed this 28th day of September 1 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Acting Commissioner of Pa 

